In consideration of the global environment, there have been proposed in recent years electric vehicles and hybrid vehicles driven by a motor that is powered by a fuel cell. Fuel cells are devices that generate electricity through an electrochemical reaction of hydrogen and oxygen. Fuel cell emissions are composed principally of water vapor, making hybrid vehicles and electric vehicles that use fuel cells very environmentally friendly.
However, fuel cells are typically characterized by low output responsiveness with respect to power demand. That is, when the accelerator is suddenly depressed, in some instances power may not be supplied rapidly in response. This is due to low responsiveness in the supply of fuel gas.
By continuously supplying a large quantity of fuel gas to the fuel cell regardless of power demand, output responsiveness can be improved, but since driving a pump etc. in order to supply fuel gas consumes energy, energy efficiency is lost.
Previously there was also proposed a method of using a fuel cell and battery in conjunction, using power from the battery to compensate for the delayed responsiveness of the fuel cell. For example, a fuel cell and battery are used as the power supply, and where a fluctuation in power demand is small enough to be met by the fuel cell, power is output by the fuel cell alone, whereas if there is a large fluctuation in power demand, power is provided by the fuel cell and battery together. The battery is charged by the fuel cell as needed.
Fuel cells are devices that are currently in development. Thus, there has not been sufficient study regarding the possibility of improving responsiveness through control thereof. Nor has there been sufficient study regarding methods of supplying power from a fuel cell and a rechargeable power source, such as a battery, used in conjunction, through optimal combination of the advantageous features of the two.